High strength galvanized steel sheet with excellent formability and method for manufacturing the same

Abstract

A high-strength hot-dip galvanized steel sheet with excellent processability is provided which has a TS of 1,200 MPa or higher, El of 13% or higher, and hole expansion ratio of 50% or higher. Also provided is a process for producing the steel sheet. The high-strength hot-dip galvanized steel sheet with excellent processability has a composition comprising, in terms of mass%, 0.05-0.5% carbon, 0.01-2.5% silicon, 0.5-3.5% manganese, 0.003-0.100% phosphorus, up to 0.02% sulfur, and 0.010-0.5% aluminum, with the remainder being iron and incidental impurities, and has a microstructure comprising, in terms of areal proportion as determined through a structure examination, 0-10% ferrite, 0-10% martensite, and 60-95% tempered martensite and containing, in terms of proportion as determined by X-ray diffractometry, 5-20% retained austenite.

Description

technical field [0001] The present invention relates to a high-strength hot-dip galvanized steel sheet with excellent workability used in industrial fields such as automobiles and electric power. In particular, it relates to a steel sheet having a tensile strength TS of 1200 MPa or more and an elongation E1 of 13% or more and having a tensile flangeability A high-strength hot-dip galvanized steel sheet with a hole expansion rate of more than 50% and a manufacturing method thereof. Background technique [0002] In recent years, improving the fuel efficiency of automobiles has become an important issue from the viewpoint of protecting the global environment. Therefore, studies are being made to reduce the weight of the vehicle body itself by increasing the strength and reducing the thickness of the steel plate used as the material of the vehicle body. However, generally, the increase in the strength of the steel sheet leads to a reduction in the ductility of the steel sheet, ...

AI Technical Summary

Problems solved by technology

However, since such DP steel or TRIP steel contains soft ferrite, a large amount of alloy elements are required to achieve high strength with a TS of 980 MPa or more, and there are ferrite and second phase phases during high strength. Increased hardness difference, poor stretch flangeability required for hole expansion, etc.

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